In general, the invention relates to a control unit for transferring electrical energy from a power source to a driven unit which may for instance be capable of converting electrical energy to a mechanical output. More particularly, the invention relates to a control unit for instituting and regulating the flow of electrical energy from a power source to such a driven unit. More specifically, the invention relates to a control unit operable with a power source and a driven unit to selectively institute current flow through one or more paths to the driven unit, to provide regulation of the amount of current flow from none to the full capacity of the power source, and/or to provide for combined integrated operation for both the institution and regulation of current flow, if desired.
It has been known for many years that a power source such as a blank of batteries may be employed to provide direct current for powering a driven unit such as a motor to run small vehicles in the nature of golf carts and industrial trucks. Except in the use of extremely sophisticated and expensive controls, anyone familiar with the operation of such vehicles is well aware of their tendencies to lurch or jerk in varying degrees upon the institution of current flow or when a power change is effected by an increase or decrease in the current flow to the motor. Such irregular or nonsmooth operating characteristics at least minimally constitute an irritation to vehicle occupants and in some instances produce dangerous safety conditions as when older persons operate golf carts or when industrial trucks are operated in close proximity to other workers or on raised loading docks.
It is also widely recognized that such vehicles have undue maintenance problems in regard to the control units which institute and regulate the current flow from a battery to the drive motor. Characteristically such control units employ a plurlaity of relatively movable solid contacts which incrementally provide variation in the current flow. The initial lurching accompanying adjustment of such control units to effect a change in current flow is noted for becoming progressively worse during operation at high load starts, as when a vehicle is started on an incline, or repetitious institution of low current flow, as when endeavors are made to inch a vehicle a short distance in one direction or another, since these conditions tend to produce arcing and heat which may damage the contacts. These problems are intensified in the higher power ranges necessary in conjunction with larger driven units such as those employed in industrial trucks wherein arcing may effect actual welding of the contacts.
The unsatisfactory performance and maintenance characteristics of the various solid contact devices which have been employed has prompted efforts to develop other types of control devices for those applications; however none have proven to be satisfactory in all respects. For example, various rheostat type devices have evolved wherein a movable contact engages a helical coil of wire. Such rheostat devices are, however, extremely limited in current carrying capacity. More recently, efforts have been made to develop solid state control units; however, cost considerations have limited the number of applications for such units.